Amex cards were originally designed for business people. The premise being that they needed a univerally recognized marque anywhere they went, and their company woulf pay the bill according to its terms.
Amex green, gold, platinum cards function based on the fact that you will pay the total amount due every billing period. If you start with a green Amex and do this for 1 year - they will upgrade you to a Gold card. If you have a Gold Card and play by their rules for their determined pweiod of time - they will invite you yo upgrade to a Platinum Card. (Which also gets you a pretty neat magazine.)
Amex also offers a card that functions like other credit cards - monthly installments, etc - I think, and I could be wrong, its referred to as their “Infinity Card.” It has its limits.
A unique feature of Amex cards is their built in purchase/guarantee coverage. Amex basically insures your purchase in addition to any warranty offered by the mechant or manufacturer. Its a good feature. Amex also can be advantaegeous with airline reservations and extras.
Amex also has some of the highest yearly fees of the industry. For some its worth it, for others its a negative.
This is a basic overview of Amex cards. Basically they expect you to pay everything off in each designated billing period.